Wireless networks are increasingly employed to provide various communication functions including voice, video, packet data, messaging and the like. Depending upon the wireless communication system, it may be desirable to provide a transceiver capable of operating on more than one frequency band. To obtain this functionality, the transceiver may be designed to employ a frequency synthesizer that generates the requisite frequency for each band to convert between the carrier radio frequency (RF) and the baseband frequency. Further, the design of the transceiver may employ a direct conversion technique or may use one or more intermediate frequencies (IFs). To generate the necessary frequencies, the frequency synthesizer may employ phase locked loop (PLL) circuitry including a voltage controlled oscillator (VCO). The choice of transceiver architecture and the operational frequencies of the VCO used by the frequency synthesizer depends on balancing a number of design constraints. For example, it may be desirable to avoid operating the VCO at frequencies that are integer multiples of the carrier frequency in order to minimize pulling effects on the VCO. Further, the operation of the VCO may result in spurious signals that depend upon the VCO's frequency of operation.
Accordingly, this disclosure is directed to a frequency synthesizer for use in a wireless communications system operating on a plurality of frequency bands that generates more than one desired frequency and minimizes interference in other wireless communications systems.